With the rapid development of information technologies and the popularization of information media such as computers, semiconductor devices have made rapid progress. In functional aspects, the semiconductor device has tended toward high integration. Accordingly, various methods haven been studied and developed in order to reduce the feature size of individual devices formed on a substrate and to maximize the performance of the devices. Among such methods, a FET (field effect transistor) fabricated through CMOS technology has the highest competitiveness because it can improve the integration degree of devices based on a silicon semiconductor technology. However, the size of the FET is scaled down as the device has become highly integrated, so the performance or reliability of the device is degraded.